1. Technical Field
The present invention generally relates to idle control for motor vehicles and, more particularly, to a method for improving the idle quality of a motor vehicle engine by applying calculated spark corrections to individual cylinders so as to counter torque imbalances.
2. Discussion
According to the prior art, spark stabilization is used under idle conditions in motor vehicle engines to reduce engine speed excursions away from a desired idle speed set point. Idle spark stabilization works in conjunction with an idle air control motor to maintain a constant idle engine speed and to counteract the effects of varying accessory loads on idle speed.
Idle spark stabilization is a short-term correction utilizing a proportional-derivative controller to act upon any deviation from desired idle speed. If the engine is operating below or above the desired idle speed, the feature advances or retards spark angle for all cylinders simultaneously, temporarily increasing or reducing the torque output of the engine, respectively. The feature improves desired idle speed tracking performance above that which can be achieved with a typical idle air control motor alone.
Although spark stabilization idle control systems are effective for improving idle speed tracking and therefore idle quality, there is room for improvement in the art. More particularly, it would be desirable to improve the idle quality of the motor vehicle engine by applying spark corrections on an individual cylinder basis to counter torque imbalances between cylinders, in addition to the spark stabilization idle control of the prior art.